In this Project 2 entitled "T cell and General Immune Responses to Influenza," we focus on general immunological biomarkers and antigen specific T cells in a continuing effort to define the immune response to influenza vaccination in volunteers from different age groups and especially utilizing the twin cohorts of SRI. We hope to establish benchmarks of immune proficiency in these different cohorts that will be predictive not just of an influenza response, but of immunological "health," or at least a component of it, in general. In Aim 1, we will continue our ongoing program to survey the blood samples of volunteers being immunized for a broad array of serum cytokines, white blood cell subsets, lymphocyte proliferation, and whole genome gene expression. Using the twin cohorts, we will be able to ask what traits are determined genetically, and of those evident in young adults, which change in older adults. Also a high priority is what traits correlate with a robust or poor response. in Aim 2 and 3, we will take advantage of recent advances in peptide-MHC tetramer technology together with our own efforts to probe more broadly and deeply into the nature of the T cell response to different influenza antigens. Thus, we will survey dozens of different T cell epitopes at once to ask whether or not there are specific changes in influenza specific T cell repertoires with age and to what extent does genetics contribute to the repertoire. We will also ask how the different influenza vaccine types influence the repertoire of responding T cells and whether or not there is a correlation between the repertoire used, and a robust or poor response. We have also been able recently to isolate antigen specific naive populations of T cells (which are in the cytokines produced in the signaling pathways utilized; in some cases, only 1 in one million cells of the CD8+ T cell pool). This gives us the ability to probe the naive repertoire of strain-specific T cells in young adults and characterize their response to different types of influenza vaccination. Lastly, in Aim 4, we propose to use "humanized" mice to test hypotheses generated in the first three aims.